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    "# 主要符号一览\n",
    "\n",
    "下面列举了本书中使用的主要符号。\n",
    "\n",
    "## 数\n",
    "\n",
    "* $x$：标量\n",
    "* $\\boldsymbol{x}$：向量\n",
    "* $\\boldsymbol{X}$：矩阵\n",
    "* $\\mathsf{X}$：张量\n",
    "\n",
    "\n",
    "## 集合\n",
    "\n",
    "* $\\mathcal{X}$：集合\n",
    "* $\\mathbb{R}$：实数集合\n",
    "* $\\mathbb{R}^n$：$n$维的实数向量集合\n",
    "* $\\mathbb{R}^{x\\times y}$：$x$行$y$列的实数矩阵集合\n",
    "\n",
    "\n",
    "## 操作符\n",
    "\n",
    "* $\\boldsymbol{(\\cdot)}^\\top$：向量或矩阵的转置\n",
    "* $\\odot$：按元素相乘，即阿达马（Hadamard）积\n",
    "* $\\lvert\\mathcal{X}\\rvert$：集合$\\mathcal{X}$中元素个数\n",
    "* $\\|\\cdot\\|_p$：$L_p$范数\n",
    "* $\\|\\cdot\\|$：$L_2$范数\n",
    "* $\\sum$：连加\n",
    "* $\\prod$：连乘\n",
    "\n",
    "\n",
    "## 函数\n",
    "\n",
    "* $f(\\cdot)$：函数\n",
    "* $\\log(\\cdot)$：自然对数函数\n",
    "* $\\exp(\\cdot)$：指数函数\n",
    "\n",
    "\n",
    "## 导数和梯度\n",
    "\n",
    "* $\\frac{dy}{dx}$：$y$关于$x$的导数\n",
    "* $\\frac{\\partial y}{\\partial x}$：$y$关于$x$的偏导数\n",
    "* $\\nabla_{\\cdot} y$：$y$关于$\\cdot$的梯度\n",
    "\n",
    "\n",
    "## 概率和统计\n",
    "\n",
    "* $P(\\cdot)$：概率分布\n",
    "* $\\cdot\\sim P$：随机变量$\\cdot$的概率分布是$P$\n",
    "* $P(\\cdot \\mid\\cdot)$：条件概率分布\n",
    "* $E_{\\cdot}\\left(f(\\cdot)\\right)$：函数$f(\\cdot)$对$\\cdot$的数学期望\n",
    "\n",
    "## 复杂度\n",
    "\n",
    "* $\\mathcal{O}$：大O符号（渐进符号）"
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